To date, network is widely used everywhere, from offices to home. The most used network system is illustrated in FIG. 1. A plurality of personal computers (PCs) 10 are successfully connected by means of a network hub 11 or a main server. The hub 11 or main server is further connected to a modem 12 such as an asymmetric digital subscriber line (ADSL) modem or a cable modem so that the computers 10 can access data from the internet via the telephone lines 13 or cables. A splitter 14 is necessary for the modem 12 to share the telephone lines 13 with the telephone 15. The splitter 14 filters out the high frequency signals to maintain high quality in telephone communication.
However, it is always a troublesome work to install a network cabling system in an office or a house without beforehand layout. There are a lot of difficulties in additional network cabling inside the floor or wall. It will be much simpler to lay the cables on the surface of the floor or the wall. Even though the cables are possibly arranged at corners, it is still unsightly and may adversely affect the pass by the floor. In an alternative network system, the networking signals are transmitted via existing electric wires. Please refer to FIG. 2 in which an AC line networking system is shown. The networking signals are transmitted via the existing AC lines 22. The power line adapters 21, each of which has a power plug at one end and an RJ45 or USB connector at the other end, are connected between the personal computers 20 and the utility power sockets 23 to establish a small local area network (LAN). Since electric wire layout is generally more popular than telephone line layout, the network system conducted via electric wires will simplify the network cabling task. U.S. Pat. No. 6,445,087 B1 assigned to the same assignee discloses such a network system, which is incorporated herein for reference.
The network system conducted via electric wires, however, suffers from the surge problem. The surge currents transmitted on the AC lines will significantly affect the communication quality of the networking signals.